GraphPad Statistics Guide

How to: Unpaired t test from raw data

How to: Unpaired t test from raw data

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How to: Unpaired t test from raw data

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1. Create data table and enter data

From the Welcome (or New Table and graph) dialog, choose the Column tab.

Choose to enter replicate values stacked in columns. Or, if you are not ready to enter your own data, choose sample data and choose: t test - unpaired.

Enter the data for each group into a separate column. The two groups do not have to have the same number of values, and it's OK to leave some cells empty.

2. Choose the unpaired t test

1.From the data table, click on the toolbar.

2.Choose t tests from the list of column analyses.

3.On the first (Experimental Design) tab of t test dialog, make these choices:

Experimental design: Unpaired

Assume Gaussian distribution: Yes.

Choose test:  Unpaired t test. Choose the Welch's correction if you don't want to assume the two sets of data are sampled from populations with equal variances, and you are willing to accept the loss of power that comes with that choice. That choice is used rarely, so don't check it unless you are quite sure.

4. On the options tab, make these choices:

Choose a one- or two-sided P value. If in doubt, choose a two-tail P value.

Choose the direction of the differences. This choice only affects the sign of the difference and the confidence interval of the difference, without affecting the P value.

Choose a confidence level. Leave this set to 95%, unless you have a good reason to change it.

3. Review the results

The t test investigates the likelihood that the difference between the means of the two groups could have been caused by chance. So the most important results are the 95% confidence interval for that difference and the P value.

Learn more about interpreting and graphing the results.

Before accepting the results, review the analysis checklist.